Certainly they work for some people but for others an intensive driving course (or crash course) is too intense! It will depend very much on the individual. But remember it’s not a short cut. You still have to learn the same amount.
I would suggest that to gain the best from learning that you allow time in between your lesson to internalise what you have learnt. Slow and steady about 2 hours per week is usually good.
In reality humans have a limited amount of concentration in one go. If you have booked an intensive course that includes about 4 hours per day over several days you can assume some of those hours would have gone to waste.
If you have some driving experience already and nearly at test standard then a short intensive might be of benefit.
If you would like any further advice please don’t hesitate to ask.